There have been conventionally investigated and developed blockers of various .alpha..sub.1 -adrenoceptors, and many compounds have been reported. As the compounds having an .alpha..sub.1 -adrenoceptor-blocking effect, for example, Arzneim. Forsh., vol. 17, 305 (1967) discloses moxisylyte hydrochloride, which is not entirely satisfactory in the effect as an .alpha..sub.1 -adrenoceptor blocker. Also, prazosin hydrochloride is used as a therapeutic agent for hypertension and dysuria, whereas it causes side effects such as orthostatic hypotension.
The conventional .alpha..sub.1 -adrenoceptor blockers are not sufficient for the treatment of the diseases mediated by the sympathetic nervous system, such as hypertension, pulmonary hypertension, congestive heart failure, myocardial ischemia, arrhythmia, angina pectoris, peripheral vascular diseases, cardiovascular disorders due to the change in vascular resistance, abnormal serum lipid, benign prostatic hypertrophy, dysuria, diabetes, glaucoma, ocular hypertension, obesity, colic convulsion, gastrointestinal dyskinesia (e.g. irritable intestinal syndromes and constipation) and central nervous diseases (e.g. impotence, depression and senile demantia). In addition, the conventional .alpha..sub.1 -adrenoceptor blockers are known to cause side effects such as orthostatic hypotension. It is therefore an object of the present invention to overcome these defects of the conventional .alpha..sub.1 -adrenoceptor blockers and provide an .alpha..sub.1 -adrenoceptor blocker which exhibits strong .alpha..sub.1 -adrenoceptor-blocking effect and causes less side effects such as orthostatic hypotension.